A variety of radio communication systems that operate in accordance with 3GPP (Third Generation Partnership Project) protocols are used. In a radio communication system that operates in accordance with LTE/SAE (Long Term Evolution/System Architecture Evolution) protocol in the 3GPP protocols, a user device performs cell searching to establish synchronization with a macro base station so as to perform radio communication. In performing cell searching, the user device, by calculating correlations between a synchronization signal transmitted by the macro base station and a replica signal stored in the user device, detects a transmission timing of the synchronization signal and a physical cell identity (PCI) so as to recognize (identify) the macro base station.